With the introduction of digitally based television transmissions set to be completed in the United States by the end of 2006, all analog based television transmissions are set to be eliminated. In order to receive such digitally based transmissions, a user will either need an High Definition television (HDTV) with an integrated digital-TV tuner or a receiver set top box (with a built in digital-TV tuner) that can be connected to an existing analog television or monitor. Because of the high cost involved in buying an HDTV, many users will opt to use a digital set top box with their older analog television to receive the digital television signals instead of buying a new television set.
One issue with digitally based television transmissions is the requirement that such television sets be capable of processing closed captioned text. Specifically, the United States government requires that many based television shows be broadcasted with closed captioning text in accordance with the Electronic Industries Association-708 (EIA-708) broadcast standard. Unfortunately, only HDTV television sets would be capable of receiving EIA-708 based text services because, the older television sets are not equipped to receive and decode such text services.
When using a set top box with an analog television or monitor, a user would then receive an HD television transmission and the EIA 708 text services for use with high definition based television signals. With a digital set top box, a user may miss out on the feature of having closed captioning appear on the display device when muting the volume of a television program. The reason for this is that the set top box is a fixed volume device, where it only outputs an audio signal at constant volume. The actual volume of the television program is controlled at the point of the display device, not the set top box, where the display device controls the emission of the audio signal (from the set top box). Therefore, set top boxes currently do not react in response to a volume muting command and do not present text services when muting occurs, and analog television devices do not display EIA 708 based text services when muted.
This same problem exists also for devices that are networked together (for example using HAVI, or AV/C) where an audio device may be physically separated from a display device. Presently, when an audio device is muted, a display device would have no way of knowing about the audio mute mode or of presenting a text service in response to such a mute mode.